Hydraulic transaxle apparatus for a four-wheel-drive vehicle and four-wheel-drive vehicle using the apparatus

ABSTRACT

An articulated vehicle with a working device has a first frame having a prime mover mounted thereon and supporting a first transaxle apparatus. The first transaxle apparatus includes an input shaft receiving power from the prime mover, a pair of first axles, and a hydrostatic transmission. The hydrostatic transmission comprises a variable hydraulic pump, a first hydraulic motor fluidly connected to the hydraulic pump via a fluid passage, and a housing with a flexible port fluidly connected to the fluid passage. The second transaxle apparatus includes a pair of second axles having different lengths and a second hydraulic motor. The second hydraulic motor is fluidly connected via piping to a directionally adjustable connection portion of the flexible port. Proximal ends of the first and second frames with respect to the vehicle are coupled to each other so that the first and second frames are rotatable around a vertical axis relative to each other when steered.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.11/033,543, filed Jan. 12, 2005, which is a divisional of U.S. patentapplication Ser. No. 10/270,378, filed Oct. 15, 2002, now U.S. Pat. No.6,845,837, issued Jan. 25, 2005, the entire disclosures of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a transaxle apparatus having a housing whichincorporates a hydrostatic transmission (HST) and a hydraulic actuatorarranged outside the housing which can be supplied with hydraulic fluidfrom the HST. More particularly, it relates to a four-wheel-drivearticulated working vehicle.

2. Related Art

A well-known articulated riding lawn mower has first and second frameswhich are mutually pivotally coupled at proximal ends thereof so as toturn relatively to each other around a vertically axial pivot steeringoperation (i.e., manipulation of a steering wheel). The first frame isequipped with a prime mover and a transaxle apparatus which supportsfirst axles driven by power from the prime mover. The second frame isequipped with a working device such as a mower device, an operatingsection, and an axle casing that supports second axles freely rotatably.P In the Japanese Patent Laid Open Gazette 2000-270651, for example, isdisclosed an articulated four-wheeled lawn mower, which includes as thefirst frame a rear frame and as the second frame a front frame. On therear frame, a hydrostatic transmission (hereinafter, “HST”) is disposed,which transfers engine power to rear wheels supported by the rear frame.Moreover, in the rear frame is disposed a power take-off shaft, whichreceives power from a pump shaft of a hydraulic pump of the HST. Thepump shaft revolves synchronously to the engine power output revolution.The revolution of the pump shaft is transferred to the mower devicesupported by the front frame.

Generally, as to each of vehicles having the above structure, while thefirst axles supported by the transaxle apparatus of the first frame(usually serving as a rear frame) is driven by the prime mover, thesecond axles supported by the axle casing of the second frame (usuallyserving as a front frame) revolve freely and not in driving associationwith the power for driving the axles of the first frame. Thus, thevehicle is a so-called two-wheel drive vehicle.

However, while the two-wheel-drive vehicle which drives only rear wheelsexhibits superior steering performance, it lacks stability when workingon a slope and roadability when running on a bad road. Further, if thevehicle is an articulated vehicle, the steering performance must beimproved because the vehicle is bent at the coupling part of the frames.Moreover, the vehicle is difficult to bail out if it becomes stuck, suchas in mud, etc.

For solving these problems, a four-wheel-drive design, which drives bothfront and rear wheels, is desirable for the articulated vehicle. Therear frame of the vehicle disclosed in the above document is providedwith an HST and a power take-off shaft for transferring power to theworking device. However, as mentioned above, since the power take-offshaft revolves synchronously with the revolution of the pump shaft, therotary speed of the pump shaft is fixed as long as the engine speed isfixed. On the other hand, the rotary speed of the rear wheels, which aredriven by the power output of the hydraulic motor, is changed variablyby a running speed changing operation which adjusts the angle of amovable swash plate of the hydraulic pump. Therefore, the power take-offshaft for driving the working device cannot be used as a front wheeldrive shaft. Even if another power take-off shaft for front-wheel-drive,whose rotation is synchronized with the power output of the HST for rearwheel drive, can be connected to the transaxle apparatus mounted in therear frame, severe limitations exist for such an arrangement to infixadditional mechanical transmission system between front and reartransaxle apparatuses, because the turning of front and rear frames mustbe permitted, as well as infixing the transmission system for theworking device drive therebetween.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide on an articulatedvehicle a transaxle apparatus for making the articulated vehicle afour-wheel-drive articulated working vehicle. The transaxle apparatusincludes a housing containing an HST and is enabled to supply hydraulicfluid from the HST to a hydraulic actuator for driving wheels arrangedoutside of the housing.

To achieve the first object, according to the transaxle apparatus of thepresent invention, a housing containing an HST is provided. The HSTcomprises a hydraulic pump receiving power from the prime mover, a firsthydraulic motor driven in response to fluid from the hydraulic pump todrive a first axle, and a center section. In the center section areprovided fluid passages, which are disposed in the housing so as tobring the hydraulic pump and the first hydraulic motor into mutualfluidal connection. Also disposed in the center section are ports, whichare located on an outer surface of the housing and fluidly connectedwith the fluid passages so as to introduce fluid flowing in the fluidpassages into a hydraulic actuator disposed outside the housing. Thefirst axle driven by the first hydraulic motor is disposed in thehousing.

The hydraulic actuator may comprise a second hydraulic motor for drivinga second axle disposed outside the housing so as to constitute afour-wheel-drive vehicle.

The center section is detachably attached to the housing, therebyadvantageously facilitating its manufacture and preventing fluid fromleaking from the fluid passages to the outside of the housing.

The ports are equipped with tubular elements for supplying pressurizedfluid (hydraulic fluid) to the hydraulic actuator (the second hydraulicmotor) arranged outside the housing. The housing is equipped withopenings for exposing the utmost ends of the tubular elements outsidethe housing. Furthermore, the tubular elements are detachably attachedto the center section.

Accordingly, flexibility of the arrangement of the elements forsupplying pressurized hydraulic fluid from the center section in thehousing to the outside of the housing in relation to other components(for example, means for transmitting power from the prime mover to aworking device) arranged between the first and second frames can beenhanced. Moreover, inexpensive parts such as a fluid hose can be usedfor the tubular elements. Since the tubular elements are easilydetached, they facilitate maintenance. Furthermore, removal of thetubular elements can change the vehicle into two-wheel-drive vehicle.

Moreover, the above-mentioned ports of the transaxle apparatus fluidlyconnect in parallel the first hydraulic motor in the housing and thesecond hydraulic motor outside of the housing to the hydraulic pump inthe housing. This structure is suitable for a vehicle which is designedso that, when the vehicle turns, distances from a turning center of thevehicle to the front and rear axles, namely, to the first axle in thehousing and the second axle out of the housing, are different from eachother so as to cause a rotary speed difference between the front andrear axles. In this structure, pressurized hydraulic fluid dischargedfrom the hydraulic pump is distributed to both of the first and secondhydraulic motors, inside and outside of the housing, in correspondenceto the rotary speed difference between the axles.

Alternatively, the ports of the transaxle apparatus may fluidly connectin series the first hydraulic motor in the housing and the secondhydraulic motor outside of the housing to the hydraulic pump in thehousing. This structure is suitable for a vehicle designed so that, whenthe vehicle turns, distances from the turning center of the vehicle tothe front and rear axles, namely, to the first axle in the housing andthe second axle outside of the housing, are substantially equal to eachother so as not to cause a rotary speed difference between the front andrear axles. According to the series connection structure compared withthe above-mentioned parallel connection structure, the entire amount offluid discharged from the hydraulic pump is supplied to the firsthydraulic motor in the housing and the second hydraulic motor outside ofthe housing as long as the hydraulic pump is revolving. Thus, even ifeither of the front or rear wheels gets stuck, as in mud, etc., and thefront or rear axle driven by one of the hydraulic motors idles, theother hydraulic motor drives the other axle using all of the fluiddischarged by the hydraulic pump, and the vehicle can be freed.

A second object of the present invention is to provide afour-wheel-drive articulated working vehicle with the above-mentionedtransaxle apparatus, including first and second frames. The first andsecond frames are coupled mutually so as to be rotated in relation toeach other around a vertically axial pivot in the coupling parttherebetween by a steering operation. A prime mover is mounted on thefirst frame, and a working device is disposed adjacent to a distal endof one of the first and second frames.

To achieve the second object, according to the vehicle of the presentinvention, the transaxle apparatus including the HST for supporting anddriving a pair of first axles serves as a first transaxle apparatusmounted on the first frame on which the prime mover is mounted. Thehydraulic motor disposed in the housing of the first transaxle apparatusserves as a first hydraulic motor. A second transaxle apparatus with asecond hydraulic motor, which supports and drives a pair of secondaxles, is mounted on the second frame. The second hydraulic motor isfluidly connected to the above-mentioned ports of the center section ofthe HST disposed in the first transaxle apparatus. As means forreceiving power from the prime mover, a rotor is disposed at thejunction between the first and second frames so as to locate a rotationaxis of the rotor on the vertical axial pivot. The lengths of the pairof first or second axles nearer to said working device than the otherpair of axles are different from each other, and a transmission elementfor drivingly connecting the prime mover to the working device crossesthe longer axle of the pair of first or second axles nearer to saidworking device.

Due to the above structures, fluid connection of the HST of the firsttransaxle apparatus to the second hydraulic motor can be ensured withoutinterfering with the transmission system from the prime mover to theworking device, thereby realizing a four-wheel-drive articulated workingvehicle.

Moreover, the four-wheel-drive articulated working vehicle is designedso that distances from the vertically axial pivot in the coupling partto an axis of the first axles and to an axis of the second axles aresubstantially equal to each other. The vehicle can be simplified byapplying the series fluid connection as the fluid connection of thefirst and second hydraulic motors through the ports to the hydraulicpump. Accordingly, the entire amount of fluid discharged from thehydraulic pump is supplied to each of the first and second hydraulicmotors as long as the hydraulic pump is revolving. Thus, even if one ofthe drive wheels gets stuck, as in mud, etc., and either the first orsecond axles driven by one of the hydraulic motors idles, the otherhydraulic motor drives the other axles using the entire amount of fluiddischarged from the hydraulic pump so that the vehicle can be freed.

These and other objects, features, and advantages of the invention willbecome more apparent upon a reading of the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a riding lawn mower as an embodiment of afour-wheel-drive articulated working vehicle according to the presentinvention.

FIG. 2 is a plan view partly in section of the vehicle of FIG. 1.

FIG. 3 is a rear view partly in section of a front transaxle apparatus10 provided in the vehicle of FIG. 1.

FIG. 4 is a plan view of the front transaxle apparatus 10 of the presentinvention from which an upper housing half 46 is removed.

FIG. 5 is a fragmentary rear view partly in section of the fronttransaxle apparatus 10 of the present invention, showing a hydraulicmotor 40 disposed therein.

FIG. 6 is a sectional left side view of the front transaxle apparatus 10of the present invention.

FIG. 7 is a right side view of a rear transaxle apparatus 20.

FIG. 8 is a plan view partly in section of the rear transaxle apparatus20 according to the first embodiment of the present invention from whichan upper housing half 246 is removed, showing that a center section 260having ports for series connection is disposed therein.

FIG. 9 is a rear view partly in section of the rear transaxle apparatus20 according to the first embodiment.

FIG. 10 is a fragmentary sectional plan view of the rear transaxleapparatus 20 according to the first embodiment, showing the fluidpassage structure formed in the center section 260 disposed therein.

FIG. 11 is a fragmentary sectional side view of the rear transaxleapparatus 20 according to the first embodiment of the present invention.

FIG. 12 is a hydraulic circuit diagram showing the hydraulic motor 240of the rear transaxle apparatus 20 according to the first embodiment ofthe present invention and the hydraulic motor 40 of the front transaxleapparatus 10 are fluidly connected to the hydraulic pump 230 of the reartransaxle apparatus 20 in series.

FIG. 13 is a hydraulic circuit diagram of the motor of FIG. 12, showinga case where the hydraulic motor 40 of the front transaxle apparatus 10is exchanged for a variable displacement type.

FIG. 14 is a rear view partly in section of the rear transaxle apparatus20 according to another embodiment having ports for series connection,where a fluid passage member 307 is passed.

FIG. 15 is a rear view partly in section of the same where a fluidpassage member 302 is passed.

FIG. 16 is a side view partly in section of the same.

FIG. 17 is a plan view partly in section of the same.

FIG. 18 is a rear view partly in section of the rear transaxle apparatus20 according to another embodiment having ports for series connection ofanother construction.

FIG. 19 is a side view partly in section of the rear transaxle apparatus20 according to another embodiment having ports for series connection offurther another construction.

FIG. 20 is a plan view partly in section of a rear transaxle apparatus20 according to a second embodiment of the present invention from whichan upper housing half 246 is removed, showing that a center section 360having ports for parallel connection is disposed therein.

FIG. 21 is a rear view partly in section of a portion of the reartransaxle apparatus 20 according to the second embodiment where a thirdpassage is passed.

FIG. 22 is a rear view partly in section of another portion of thetransaxle of FIG. 21 where a fourth passage is passed.

FIG. 23 is a fragmentary sectional plan view of the rear transaxleapparatus 20 according to the second embodiment, showing fluid passagestructure formed in the center section 360.

FIG. 24 is a fragmentary sectional side view of the rear transaxleapparatus 20 according to the second embodiment.

FIG. 25 is a hydraulic circuit diagram showing the hydraulic motor 340of the rear transaxle apparatus 20 according to the second embodimentand the hydraulic motor 40 of the front transaxle apparatus 10 arefluidly connected in parallel to the hydraulic pump 230 of the reartransaxle apparatus 20.

FIG. 26 is a plan view partly in section of a four-wheel-drivearticulated working vehicle in which front transaxle apparatuses 400Land 400R having respective hydraulic motors are provided to right andleft front wheels, respectively.

FIG. 27 is a rear view partly in section of the right and left fronttransaxle apparatuses 400L and 400R provided to the working vehicle.

FIG. 28 is a plan view partly in section of the front transaxleapparatuses 400R (400L) provided to the working vehicle.

FIG. 29 is a hydraulic circuit diagram showing that a hydraulic motor240 of the rear transaxle apparatus 20 according to the first embodimentof the present invention and a circuit which fluidly connects hydraulicmotors 440 of both the front transaxle apparatuses 400L and 400R to eachother in parallel are fluidly connected in series to the hydraulic pump230 of the rear transaxle apparatus 20.

FIG. 30 is a hydraulic circuit diagram of the present invention in acase that variable displacement hydraulic motors serve as both thehydraulic motors 440.

FIG. 31 is a hydraulic circuit diagram showing the hydraulic motor 240of the rear transaxle apparatus 20 according to the first embodiment andthe hydraulic motors 440 of both the front transaxle apparatuses 400Land 400R are fluidly connected in series to the hydraulic pump 230 ofthe rear transaxle apparatus 20.

FIG. 32 is a hydraulic circuit diagram showing the hydraulic motor 240of the rear transaxle apparatus 20 according to the second embodiment ofthe present invention and the hydraulic motors of both the fronttransaxle apparatuses 400L and 400R are fluidly connected in parallel tothe hydraulic pump 230 of the rear transaxle apparatus 20.

FIG. 33 is a hydraulic circuit diagram showing the hydraulic motor 240of the rear transaxle apparatus 20 according to the second embodiment ofthe present invention and a circuit, which fluidly connects in seriesthe hydraulic motors of both the front transaxle apparatuses 400L and400R to each other, are fluidly connected in parallel to the hydraulicpump 230 of the rear transaxle apparatus 20.

DETAILED DESCRIPTION OF THE INVENTION

Description will be given of a four-wheel-drive articulated workingvehicle according to the present invention.

FIGS. 1 and 2 show a working vehicle equipped at a front portion thereofwith a mower device 3 serving as a working device. A front frame 11 isprovided with a front transaxle apparatus from which front wheel axles12L and 12R are extended in a transverse direction and fixed torespective front wheels 13. A rear frame 21 is provided with a reartransaxle apparatus from which rear wheel axles 22L and 22R are extendedin a transverse direction and fixed to respective rear wheels 23.

A rear end portion of the front frame 11 is horizontally rotatablycoupled to a front end portion of the rear frame 21 through a couplingpart 50. Coupling part 50 constitutes a pivot point of rotation of boththe frames. Thus, the working vehicle including the horizontallyturnable front and rear frames 11 and 21 is bendable at the intermediateportion thereof, thereby being a so-called articulated vehicle.

A steering column 14, a steering wheel 4, and a pedal 15 are arranged ina front portion of front frame 11, and a seat 9 is disposed behindsteering column 14, thereby constituting an operation part 16 on frontframe 11. Mower device 3 is vertically movably provided at a distal endof front frame 11, that is, at a downwardly forward position fromoperation part 16. Mower device 3 is driven by an engine 5.

As shown in FIGS. 1 and 2, on rear frame 21 is disposed engine 5 coveredwith a bonnet 8. A rear transaxle apparatus is arranged under engine 5.

On the rear frame 21 end, a first engine output pulley 94 is fixed to anoutput shaft 93 of engine 5, an HST input pulley 292 is fixed to a pumpshaft 231 of a hydraulic pump incorporated in the rear transaxleapparatus, and a second engine output pulley 96 (shown in FIG. 1) isfixed to output shaft 93 under first engine output pulley 94.

On the front frame 11 end, a working device drive power input pulley 111is fixed to a power input shaft 112 of mower device 3 as a workingdevice, and an idle pulley 98 is rotatably supported through a bearing(not shown) on a support shaft 97 suspended from front frame 11.

Moreover, as shown in FIGS. 1 and 2, regarding coupling part 50, acylindrical pivotal connector 28 is disposed on the laterally middlefront end of rear frame 21 and not-relatively rotatably supports a jointshaft 55 in the vertical direction. A platy pivotal connector 18, whichis U-shaped in side view, is pivotally coupled to joint shaft 55. Thus,rear frame 21 and front frame 11 are pivotally coupled so as to behorizontally turnable. In this way, pivotal connectors 18 and 28 areprovided at the respective proximal ends of frames 11 and 21, each ofwhich faces to the proximal side of the vehicle, and are pivotallyconnected to each other through joint shaft 55 so as to constitutecoupling part 50. Thus, both frames 11 and 21 are arranged in tandem andcoupled so as to be turnable around joint shaft 55, thereby enabling thevehicle to be steered.

A lower end of joint shaft 55 is extended below pivotal connector 18 soas to support a power output pulley 57 and a power input pulley 56rotatably thereon through bearings (not shown).

As shown in FIGS. 1 and 2, on rear frame 21 end, a rear drivetransmission belt 92 is wound around the first engine output pulley 94and HST input pulley 292, and a first working-device drive transmissionbelt 58 is wound around the second engine output pulley 96 and powerinput pulley 56.

On front frame 11 end, second working-device drive transmission belt 59is wound around an idle pulley 98 (FIG. 2), a working-device drive powerinput pulley 111, and power output pulley 57.

Due to this construction, engine output is transmitted to HST inputpulley 292 through rear drive transmission belt 92 from first engineoutput pulley 94 so as to rotate pump shaft 231. The engine output isalso transmitted to working-device drive power input pulley 111 throughsecond engine output pulley 96, first working-device drive transmissionbelt 58, power input pulley 56, power output pulley 57 integrallyrotating power input pulley 56, and second working-device drivetransmission belt 59, so as to rotate a power input axis 112, therebyrotating mowing blades 17.

As shown in FIG. 2, at a position shifted leftward from lateral middleof front frame 11 is disposed front transaxle apparatus, which supportsleft and right front wheel axles 12R and 12L so as to extend right frontwheel axle 12R longer than left wheel axle 12L.

As shown in FIGS. 2 and 3, a pair of left and right collars 99 a and 99b are freely rotatably on right front wheel axle 12R at a substantiallylaterally middle position of front frame 11. The lower surfaces ofsecond working-device drive transmission belt 59 comes into contact withthe respective upper surfaces of collars 99 a and 99 b.

Hence, front transaxle apparatus supports the pair of axles whoselengths are different from each other, and second working-device drivetransmission belt 59, serving as a transmission element for drivinglyconnecting engine 5 and mower device 3 to each other, crosses the longeraxle of the pair; in other words, second working-device drivetransmission belt 59 changes direction by contacting collars 99 a and 99b on the longer axle.

In this way, second working-device drive transmission belt 59 passesabove front wheel axle 12R so as not reduce the road clearance.Moreover, since collars 99 a and 99 b are idled, second working-devicedrive transmission belt 59 is not damaged by friction.

Next, description will be given of the front transaxle apparatus. Asshown in FIG. 6, an upper housing half 46 and a lower housing half 47are vertically joined to each other so as to form one housing, whichprovides the external appearance of the front transaxle apparatus 10 andcontains within its interior a fluid sump and for incorporating thehydraulic motor, etc.

As shown in FIG. 4, a counter shaft 139, on which a reduction-gear train135 is freely provided, divides the hollow interior of the housing intoa first chamber 10 a, which incorporates a differential gear unit 120,and a second chamber 10 b, which incorporates a hydraulic motor 40.Driving force of hydraulic motor is transmitted to differential gearunit 120 through reduction-gear train 135.

As shown in FIG. 5, hydraulic motor is integrally disposed within fronttransaxle apparatus. On a vertical portion of center section 62 isformed a motor mounting surface 63 m (shown in FIG. 16) on which acylinder block 43 is rotatably and slidably supported. A plurality ofpistons 42 are reciprocally movably fitted through respective biasingsprings into a plurality of cylinder bores in cylinder block 43. Athrust bearing 44 a of a fixed swash plate 44 abuts against the heads ofpistons 42. An opening 44 b is provided in the center of fixed swashplate 44 so as to allow motor shaft 41 to pass therethrough. Fixed swashplate 44 is fixedly sandwiched between upper housing half 46 and lowerhousing half 47.

Motor shaft 41 is rotatably supported by a sealed bearing 45 held on thejoint surface between upper housing half 46 and lower housing half 47.Motor shaft 41 is not-relatively rotatably engaged with cylinder block43 so as to be disposed horizontally on the rotary axis of cylinderblock 43 and serve as an output shaft.

In this way, front transaxle apparatus 10 contains an axial piston typehydraulic motor 40.

Moreover, as shown in FIG. 6, a pair of first and second kidney ports 62a and 62 b are formed in motor mounting surface 63 m formed on thevertical portion of center section 62. First and second kidney ports 62a and 62 b are connected to, respectively, horizontal first and secondfluid passages 53 a and 53 b bored within center section 62. As shown inFIG. 4, first fluid passage 53 a and second fluid passage 53 b areconnected to respective caps 54 a and 54 b to which hydraulic hoses areconnected. Thus, hydraulic motor 40 is fluidly connected to hydraulicpump 230 through hydraulic hoses (not shown).

As shown in FIG. 5, a bypass operation lever 65 for opening first fluidpassage 53 a and second fluid passage 53 b to the fluid sump is disposedabove upper housing half 46 in order to enable the axles (12L and 12R)to idle when the vehicle is towed. Bypass operation lever 65 is fixed ata basal portion thereof to an upper end of a vertical bypass lever shaft66 rotatably supported by an upper wall of upper housing half 46. Bypasslever shaft 66 extends at a lower end thereof to the interior of centersection 62 so as to be horizontally slidably in center section 62. Aflat surface 66 a is formed in a lower end side of bypass lever shaft 66so as to contact an end face of a push pin 67 which is allowed tocontact the rotationally sliding surface of cylinder block 43.

As shown in FIG. 6, a feeding-and-discarding port 46 a is formed in theupper portion of upper housing half 46 so as to enable hydraulic fluidto be fed or discharged from and to a reservoir tank (not shown).

As shown in FIGS. 4 and 5, a drive output gear 131 is fitted with splineonto an end of motor axis 41 opposite to center section 62 so as to berotated integrally with motor shaft 41. On the side of drive output gear131 facing section 62 is integrally formed a brake rotor 133 whosediameter is larger than that of drive output gear 131. Brake rotor 133is sandwiched between brake pads 134 a and 134 b (FIG. 4) so as to brakerotating motor shaft 41.

As shown in FIG. 4, a counter shaft 139 is arranged parallel to motorshaft 41, a wide, small diameter gear 137 fits loosely on counter shaft139, and a large diameter gear 136 is engaged with a toothed sideportion of small diameter gear 137, thereby forming reduction-gear train135.

Regarding reduction-gear train 135, while large diameter gear 136engages with drive output gear 131, small diameter gear 137 engages witha ring gear 121 of differential gear unit 120, thereby transmittingdriving force of motor shaft 41 to differential gear unit 120 throughreduction-gear train 135.

Moreover, differential gear unit 120 comprises ring gear 121, whichengages with small diameter gear 137 of reduction-gear train 135,pinions 123, which are rotatably supported by respective pinion shafts122 which project inward from an inner periphery of ring gear 121, andside gears 124 fixed to respective front wheel axles 12L and 12R andlaterally engaged with each of pinions 123. Due to this construction,the driving force from motor shaft 41 is transmitted to front wheelaxles 12L and 12R through reduction-gear train 135, ring gear 121,pinions 123, and side gears 124.

As shown in FIGS. 4 and 5, an end of motor axis 41, which is opposite tocylinder block 43, is extended outside of the housing so as to befixedly provided thereon with a cooling fan 191 for cooling fluidcollected in the front transaxle apparatus.

Description will now be given of the rear transaxle apparatus. As shownin FIG. 2, hydraulic motor 40 incorporated in front transaxle apparatus10, which drives front wheel axles 12L and 12R, is fluidly connectedthrough hydraulic hoses 81 a and 81 b to a hydraulic motor incorporatedin the rear transaxle apparatus 20, which drives rear wheel axles 22Land 22R.

As shown in FIGS. 8 and 9, rear transaxle apparatus comprises a housingwhich is formed by an upper housing half and a lower housing half 247vertically separably joined to each other so as to form a hollowinterior into which the hydraulic motor, etc., is incorporated.

The housing forms a bearing portion for a later-discussed motor shaft241 on the joint surface thereof between housing halves 246 and 247, andforms a bearing portion for journaling rear wheel axles 22L and 22R inthe upper housing half above the joint surface. Rear wheel axles 22L and22R are differentially connected at inner ends thereof to each otherthrough a differential gear unit 220, and extended outward fromrespective left and right outside walls of the housing.

As shown in FIG. 8, rear transaxle 20 apparatus is integrally formedtherein with an internal wall 248 which divides the inner space of reartransaxle 20 apparatus into first and second chambers 20 a and 20 b. Infirst chamber 20 a is disposed an HST 290, and in second chamber 20 bare disposed a drive train 249 comprising a gear train which transmitspower to differential gear unit 220 from motor shaft 241, differentialgear unit 220, and inner side ends of rear wheel axles 22L and 22R.

Internal wall 248 comprises a longitudinal portion parallel to rearwheel axles 22L and 22R, and a perpendicular portion extendedperpendicularly to the longitudinal portion. These two portions areprovided continuously so as to arrange first chamber 20 a adjacent tosecond chamber 20 b. An upper wall portion of internal wall 248 extendsdownward from an inner upper wall surface of upper half housing 246, anda lower portion of internal wall 248 rises from the inner bottom surfaceof lower half housing 247 through the joint surface. By joining upperand lower housings 246 and 247, end faces of both the upper and lowerwall portions are also joined to each other so as to form internal wall248, thereby dividing the inner space into first and second chambers 20a and 20 b which are independent of each other.

In the housing, first chamber 20 a is disposed in front of rear wheelaxle 22R and on a lateral side of drive train 249 which transmits powerto differential gear unit 220 from motor shaft 241.

In first chamber 20 a is detachably settled a center section 260 of theHST. A longitudinal portion of center section 260 is extendedrectangularly to rear wheel axles 22L and 22R, and a vertical surface isformed on a front portion of the longitudinal portion so as to serve asa motor mounting surface 260 m, onto which the hydraulic motor ismounted. A horizontal surface is formed on the rear portion of centersection 260 so as to serve as a pump mounting surface 260 p, onto whichthe hydraulic pump is mounted. In the center of pump mounting surface260 p is vertically supported a pump shaft 231.

Description will now be given of the hydraulic pump arranged on centersection 260.

As shown in FIG. 9, a cylinder block 233 is rotatably and slidablydisposed on pump mounting surface 260 p which is formed at thehorizontal portion of center section 260.

Pistons 232 are reciprocally movably fitted through respective biasingsprings into a plurality of cylinder bores in cylinder block 233. Athrust bearing 234 a of a movable swash plate 234 abuts against theheads of pistons 232. An opening 234 b is provided at the center ofmovable swash plate 234 so as to allow a pump shaft 231 to passtherethrough. A control arm 238 engages with a side of movable swashplate 234 so that a tilt angle of movable swash plate 234 is adjusted byrotating a control shaft 237 serving as a rotary shaft of control arm238.

In order that pump shaft 231 may function as an input shaft, pump shaft231 is rotatably supported by a bearing 235 engaged in an opening 236formed above first chamber 20 a in upper half housing 246 and isnot-relatively rotatably engaged with cylinder block 233, thereby beingarranged vertically on the rotary axis of cylinder block 233.

In this way, an axial piston type variable displacement hydraulic pumpis constructed in rear transaxle apparatus.

As shown in FIG. 9, the upper end of pump shaft 231 projects outwardlyfrom the rear transaxle apparatus. An HST input pulley 292 and a coolingfan 291 are fixed onto the upper end of pump shaft 231. Thus, whilecooling the hydraulic fluid accumulated in rear transaxle apparatus 20by cooling fan 291, driving force of the engine is inputted into HSTinput pulley 292 through a transmission element so as to rotate pumpshaft 231.

Description will now be given of the hydraulic motor 240 arranged oncenter section 260.

As shown in FIG. 8, a cylinder block 243 is rotatably and slidablydisposed on motor mounting surface 260 m which is formed at the verticalportion of center section 260.

A plurality of pistons 242 are reciprocally movably fitted into aplurality of cylinder bores in cylinder block 243 through respectivebiasing springs. The heads of pistons 242 abut against a thrust bearing244 a of a fixed swash plate 244 which is fixedly sandwiched betweenupper housing half 246 and lower housing half 247. An opening 244 b isprovided in the center of fixed swash plate 244 so as to allow motorshaft 241 to pass therethrough.

In order that motor shaft 241 may function as an output shaft, motorshaft 241 is rotatably supported by a sealed bearing 245 sandwichedbetween upper housing half 246 and lower housing half 247, and isnot-relatively rotatably engaged with cylinder block 243, thereby beingarranged horizontally on the rotary axis of cylinder block 243.

In this way, an axial piston type fixed displacement hydraulic motor isconstructed in rear transaxle apparatus 20.

Moreover, as shown in FIG. 8, the end portion of motor shaft 241opposite to center section 260 is fitted with a drive output gear 212 inspline fitting such that drive output gear 212 rotates with motor shaft241. The portion of motor shaft 241 outward from drive output gear 212is fitted with a brake rotor 213 in spline fitting. By pressing brakerotor 213 between brake pads 214 a and 214 b, rotating motor shaft 241is braked. In this embodiment, as mentioned above, brake devicesincluding brake rotor 213 are provided in respective transaxleapparatuses 10 and 20, although it may be considered that at least oneof transaxle apparatuses 10 and 20 is provided therein with the brakedevice. These two brake devices can be used effectively, namely, onebrake device is for braking during running of the vehicle, and the otherfor a brake at the time of parking. With this structure, a mechanicallink interlocked with a running brake pedal and a mechanical linkinterlocked with a parking brake lever are distributed so as to besimplified. Moreover, the braking effect may be enhanced if both thefront and rear brake devices are connected to the running brake pedal soas to be actuated for braking simultaneously.

As shown in FIG. 8, a counter shaft 239 is arranged parallel to motorshaft 241, a wide, small diameter gear 217 fits loosely on counter shaft239, and a large diameter gear 216 is engaged on a toothed side of smalldiameter gear 217, thereby constituting a reduction-gear train 215.

Regarding reduction-gear train 215, large diameter gear 216 engages withdrive output gear 212, small diameter gear 217 engages with a ring gear221 of a differential gear unit 220, thereby transmitting the drivingforce from motor shaft 241 to differential gear unit 220 throughreduction-gear train 215.

Moreover, differential gear unit 220 comprises ring gear 221, whichengages with small diameter gear 217, pinions 223 rotatably supported byrespective pinion shafts 222 which project inward from an innerperiphery of ring gear 221, and left and right side gears 224 fixed torespective rear wheel axles 22L and 22R and engaged with each of pinions223. Due to this construction, the driving force of motor shaft 241 istransmitted to rear wheel axles 22L and 22R through reduction-gear train215, ring gear 221, pinions 223, and side gears 224.

Description will now be given of a hydraulic circuit structure inside ofcenter section 260 and a manifold block 268, which is attached to theundersurface of center section 260.

First, a first embodiment of a hydraulic circuit structure is described.According to the first embodiment, hydraulic motor 40 in front transaxleapparatus 10 and hydraulic motor 240 in rear transaxle apparatus 20 arefluidly connected in series to hydraulic pump in 230.

As shown in FIG. 8, into pump mounting surface 260 p in the horizontalportion of center section 260 are bored a first kidney port 261 a and asecond kidney port 261 b opposite to each other. These kidney ports 261a and 261 b are open at a position above which openings of the cylinderbores of cylinder block 233 pass.

As shown in FIG. 10, into motor mounting surface 260 m in the verticalportion of center section 260 are bored a first kidney port 262 a and asecond kidney port 262 b opposite to each other. These kidney ports 262a and 262 b are open at a position where openings of the cylinder boresof cylinder block 243 pass leftward.

As shown in FIGS. 9 to 11, in center section 260 are bored an upperfirst fluid passage 271 and a lower second fluid passage 272 parallel toeach other in the longitudinal direction of center section 260. Firstfluid passage 271 connects first kidney port 261 a at pump mountingsurface 260 p to first kidney port 262 a at motor mounting surface 260m. Second fluid passage 272 is connected at the front end thereof tosecond kidney port 262 b at motor mounting surface 260 m.

Moreover, as shown in FIGS. 9 and 10, manifold block 268 is attached tothe undersurface of center section 260. In manifold block 268 from aside surface thereof are bored a third fluid passage 273 and a fourthfluid passage 274 parallel to each other and perpendicular to first andsecond fluid passages 271 and 272. Into openings of third and fourthfluid passages on the left side surface of manifold block 268 are fittedrespective caps 283 and 284 so as to constitute connection ports 273 aand 274 a. As shown in FIG. 9, ends of caps 283 and 284 project outwardfrom lower housing half 247 so as to be connected to hydraulic hoses(not shown) outside of lower housing half 247. The axes of connectionports 273 a and 274 a are disposed in a substantially horizontal plane,namely, they are not slant upward or downward, thereby facilitating theconnection work of piping comparatively. That is, the arrangement ofconnection ports 273 a and 274 a in the horizontal plane solves theproblems of the reduction of the ground clearance in the case of pipingwith downward ports and interference of piping with a transmission beltor a frame in the case of piping with upward ports. However, if theminimum requirement is achieved that heads of caps 283 and 284 on thehousing of rear transaxle apparatus 20 mounted on the vehicle areprevented from interfering with surrounding instruments, ports 273 a and274 a are accepted to be disposed on any of top, bottom, front, rear,left and right end surfaces of the housing and in any direction.

Moreover, as shown in FIG. 9, between center section 260 and manifoldblock 268 are bored a vertical fifth fluid passage 275, which connectssecond fluid passage 272 to third fluid passage 273, and a verticalsixth fluid passage 276, which connects second kidney port 262 b in pumpmounting surface 260 p to fourth fluid passage 274.

Incidentally, a bypass operation lever (not shown) for opening firstfluid passage 271 and second fluid passage 272 to the fluid sump isdisposed at rear transaxle apparatus 20 in order to enable axles 22L and22R to idle when the vehicle is towed.

Due to the above-mentioned fluid passages, the hydraulic motor in thefront transaxle apparatus 10 and the hydraulic motor 240 in the reartransaxle apparatus 20 are fluidly connected in series to the hydraulicpump 230 in the rear transaxle apparatus 20.

That is, as shown in FIG. 2, hydraulic hose 81 a connects cap 54 a onthe front transaxle apparatus 10 to cap 283 on rear transaxle apparatus20, and hydraulic hose 81 b connects cap 54 b on front transaxleapparatus 10 to cap 284 on rear transaxle apparatus 20, thereby forminga hydraulic circuit shown in FIG. 12. The kind of fluid communicationmeans between the front and rear transaxle apparatuses 10 and 20 is notlimited. However, like hoses 81 a and 81 b according to this embodiment,the means is preferably flexible and resistant to considerably highpressure so as not to interfere with the bending of the vehicle body.

According to the hydraulic circuit shown in FIG. 12, in center section260 arranged in rear transaxle apparatus 20, first kidney port 261 a ofpump-mounting-surface 260 p is connected through first fluid passage 271to first kidney port 262 a of motor mounting surface 260 m. Also, secondkidney port 262 b in center section 260 of motor mounting surface 260 mis connected to first kidney port 62 a in center section 62 of fronttransaxle apparatus 10 to motor mounting surface 63 m through a stringof fluid passages 299 a which consists of second fluid passage 272,fifth fluid passage 275, third fluid passage 273, hydraulic hose 81 a,and first fluid passage 53 a provided in center section 62 of fronttransaxle apparatus 10.

Second kidney port 62 b formed in center section 62 of front transaxleapparatus 10 to is connected to second kidney port 261 b formed inpump-mounting-surface 260 p in center section 260 through second fluidpassage 53 b provided in center section 62, hydraulic hose 81 b, and astring of fluid passages 299 b which consists of fourth fluid passage274 and sixth fluid passage 276 in the rear transaxle apparatus 20.

As mentioned above, in the hydraulic circuit structure according to thefirst embodiment, hydraulic motors 40 and 240, which are arranged infront and rear transaxle apparatuses 10 and 20, respectively, arefluidly connected in series to hydraulic pump 230. This in seriesconnection form is suitable for an articulated vehicle in which couplingpart 50 serves as a turning center of the vehicle and is arranged at anequidistant position from both the front and rear axles of the vehicle.

In this way, in front transaxle apparatus 10 and rear transaxleapparatus 20 are driven front wheel axles 12L and 12R and rear wheelaxles 22L and 22R, respectively, thereby realizing a four-wheel-drivevehicle which is excellent in both steering performance and runningperformance over bad ground conditions.

Especially, a four-wheel-drive working vehicle provided with the inseries hydraulic connection has the capability of freeing its runningwheels from mud. For example, even if the vehicle travels in a swamp anda front wheel is stuck in mud, hydraulic fluid discharged from hydraulicpump 230 bypasses hydraulic motor 40 in front transaxle apparatus 10 soas to idle the unloaded front wheels, and then flows into hydraulicmotor 240 in rear transaxle apparatus 20 so as to drive the loaded rearwheels, whereby the vehicle can escape from the mud smoothly.

Alternatively, caps 283 and 284 may be connected mutually through ahydraulic hose bypassing hydraulic motor 40 so as to make arear-wheel-drive vehicle which drives with only the driving force ofhydraulic motor 240 in rear transaxle apparatus.

When the rotary speed (peripheral speed) of front wheel axles 12L and12R is substantially identical to that of rear wheel axles 22L and 22R,hydraulic motors 20 and 240 in respective front and rear transaxleapparatuses 10 and 20 preferably have the same displacement (amount ofdischarge). With this composition, the same reduction gears may beapplicable to both front and rear transaxle apparatuses 10 and 20. Ofcourse, hydraulic motors of different volume can also be applied in thiscase, however, the mechanical deceleration ratio of front transaxleapparatus must be different from that of rear transaxle apparatus so asto substantially equalize the rotary speed (peripheral speed) of frontwheel axles 12L and 12R with that of rear wheels axles 22L and 22R.

In addition, as shown in FIG. 13, front transaxle apparatus for drivingthe front wheels may be modified so that the tilt angle of swash plate44 c of hydraulic motor is adjustable and swash plate 44 c isinterlockingly connected to steering wheel 4 through a wire, a link, orsimilar structure so as to correlate the tilt angle of swash plate 44 cand the turning angle of steering wheel 4, thereby increasing the rotaryspeed of the front wheel axles.

This structure is particularly effective for improving steeringperformance of a vehicle having an Ackerman type steering device or achassis layout wherein a difference of rotary speed is generated betweenthe front wheels and the rear wheels at the time of left or rightturning, namely, coupling part 50 is not located equidistant from thefront and rear axles of the vehicle.

Thus, regarding vehicles having the front and rear transaxle apparatuseswith a layout wherein a difference of rotary speed is generated betweenthe front wheels and rear wheels at the time of turning, and fluidlyconnecting in series the hydraulic motors in both the transaxleapparatuses, steering performance can be improved by making thehydraulic motor which actuates steerable wheels (the front wheels)variable in displacement, and increasing the rotary speed of thishydraulic motor in correspondence to the angle of the steering wheel.

Moreover, in hydraulic circuit shown in FIGS. 12 and 13, bypass valves40 v and 240 v are provided to front and rear hydraulic motors 40 and240, respectively, so that the fluid passages are opened to the fluidsump by the above-mentioned bypass operation lever, thereby enablingtowage of the vehicle. Towing the vehicle can be achieved if at leastone of front and rear transaxle apparatuses 10 and 20 is provided witheither bypass valve 40 v or 240 v, respectively. However, according tothis embodiment, both front and rear transaxle apparatuses 10 and 20 areprovided with respective bypass valves 40 v and 240 v. Therefore, at thetime of assembling, extraction of air can be done from each transaxleapparatus and 20 comparatively easily. Moreover, the vehicle can betowed even in low-temperatures and with high consistency of hydraulicfluid, because hydraulic fluid discharged from each of the idlinghydraulic motors 40 and 240 is bypassed near motor 40 or 240 so as notto be considerably resistant to towage of the vehicle.

Next, description will be given of another embodiment of a hydrauliccircuit structure in rear transaxle apparatus 20 according to FIGS. 14to 17. The same members or members having the same functions of theabove-mentioned embodiment are indicated by the same numerals, anddescription thereof is omitted.

As shown in FIG. 16, a fluid passage 301 is bored in center section 260substantially in parallel to fluid passage 271. As shown in FIGS. 16 and17, one of ends of fluid passage 301 is connected to second kidney port262 b opening at motor mounting surface 260 m. As shown in FIGS. 15 to17, a substantially vertical hole 301 a is bored downward from the otherend of fluid passage 301 to the lower surface of center section 260. AnL-shaped fluid passage member 302 penetrated by an L-shaped fluidpassage is slidably rotatably inserted at its top portion into hole 301a through an O-ring so as to connect the L-like passage therein to fluidpassage 301 in center section 260. As shown in FIGS. 15 and 17, a cap303 having an axially penetrating fluid passage is slidably insertedsubstantially horizontally through an opening 351 a of a lower housinghalf 351 into the housing of rear transaxle 20, and fitted at an innerend thereof into a lower opening of fluid passage member 302 so as toconnect the axial fluid passage of cap 303 to the L-shaped fluid passagein fluid passage member 302. An open outer end of the fluid passage incap 303 is disposed out of the housing of rear transaxle 20 so as toserve as a connection port 302 a, to which a pipe connecter 303 a isfitted for connecting hydraulic hose 81 a (see FIG. 13) to hydraulicmotor 40 in front transaxle 10.

On the other hand, as shown in FIG. 16, a fluid passage 304 is bored incenter section 260 substantially in parallel to fluid passage 271. Asshown in FIGS. 14, 16 and 17, a vertically slant fluid passage 305 isbored perpendicularly to fluid passage 304 when viewed in plan. One ofends of fluid passage 305 is connected to second kidney port 261 bopening at pump-mounting-surface 260 p, and the other end thereof isconnected to fluid passage 304. A substantially horizontal fluid passage306 is bored perpendicularly to fluid passage 304, and one of ends offluid passage 306 is connected to the end of fluid passage 304. Asubstantially vertical hole 306 a is bored from the other end of fluidpassage 306 to the lower surface of center section 260. An L-shapedfluid passage member 307 penetrated by an L-shaped fluid passage isslidably rotatably inserted at a top portion thereof into hole 306 athrough an O-ring. A cap 308 having an axially penetrating fluid passageis slidably inserted substantially horizontally through an opening 351 bof lower housing half 351 into the housing of rear transaxle 20, andfitted at an inner end thereof into a lower opening of fluid passagemember 307 so as to connect the axial fluid passage of cap 308 to theL-shaped fluid passage in fluid passage member 307. An open outer end ofthe fluid passage in cap 308 is disposed out of the housing of reartransaxle 20 so as to serve as a connection port 307 a, to which a pipeconnecter 308 a is fitted for connecting hydraulic hose 81 b (see FIG.13) to hydraulic motor 40 in front transaxle 10.

Accordingly, first kidney port 261 a opening at pump mounting surface260 p is communicated through fluid passage 271 with first kidney port262 a opening at motor mounting surface 260 m. Second kidney port 262 bopening at motor mounting surface 260 m is communicated through fluidpassages 301 and the fluid passage in fluid passage member 302 withconnection port 302 a. Second kidney port 261 b at pump-mounting-surface260 p is communicated through fluid passages 305, 304, 306 and the fluidpassage in fluid passage member 307 with connection port 307 a.

Therefore, by connecting pipe connecter 303 a (connection port 302 a) tohydraulic hose 81 a, and by connecting pipe connecter 308 a (connectionport 307 a) to hydraulic hose 81 b, hydraulic motor 240 in reartransaxle apparatus 20 and hydraulic motor 40 in front transaxleapparatus 10 are fluidly connected in series to hydraulic pump 230 inrear transaxle apparatus 20, similarly to the above-mentionedembodiment.

With regard to the above-mentioned embodiment, manifold block 268 isprovided below center section 260, and a filter 250 is provided belowmanifold block 268. However, with regard to the present embodiment,manifold block 268 is not provided, and the fluid passages in fluidpassage members 302 and 307 are offset from a filter 350 when viewed inplan. Accordingly, the distance between the lower end of center section260 and the bottom surface of the lower housing half can be reduced bythe thickness of the manifold block, thereby miniaturizing reartransaxle apparatus 20.

Furthermore, the fluid passage members 302 and 307 are rotatable againstcenter section 260, and caps 303 and 308 are slidable against lowerhousing half 351, thereby reducing the accuracy of boring holes 301 a,306 and 306 a in center section 260, and of boring holes 351 a and 351 bin lower housing half 351. Further, the rotation of caps 303 and 308against lower housing half 351, or the like, can adjust the directionsof pipe connectors 303 a and 308 a so as to optimize the piping ofhydraulic hoses 81 a and 81 b.

Next, description will be given of another embodiment of a hydrauliccircuit structure in rear transaxle apparatus 20 shown in FIG. 18. Inthis embodiment, fluid passage member 302 comprises a substantiallyvertical fluid passage member 302 b and a substantially horizontal fluidpassage member 302 c. Fluid passage member 302 b is penetrated by asubstantially vertical fluid passage. Screw threads are formed on aninner surface of substantially vertical hole 301 a in center section260, and on an outer surface of an upper portion of fluid passage member302 b, respectively. The threaded upper portion of fluid passage member302 b is screwed into hole 301 a so as to be connect the substantiallyvertical fluid passage therein to hole 301 a. Fluid passage member 302 cis disposed below center section 260. Fluid passage member 302 c isbored therein with a substantially horizontal hole having an outwardlyopening end into which the inner end of cap 303 is fitted so as toconnect the substantially horizontal fluid passage in cap 303 to thesubstantially horizontal fluid passage in fluid passage member 302 c. Asubstantially vertical penetrating hole 302 d is formed in one endportion of fluid passage member 302 c opposite to cap 303. A lower endof fluid passage member 302 b is slidably rotatably inserted through anO-ring into an upper end of hole 302 d. An open lower end of hole 302 dis closed with a lid 302 e. Accordingly, an L-shaped passage is formedbetween hole 301 a in center section 260 and connecting port 302 a incap 303 out of the housing of rear transaxle 20. The other members areconstructed in the same way as the above-mentioned embodiment shown inFIG. 15.

According to this construction, the same effect can be obtained as theabove-mentioned embodiment shown in FIG. 15. Furthermore, in thisembodiment, the members 302 b and 302 c constituting fluid passagemember 302 can be formed easily. In addition, fluid passage member 307also can be divisionally constructed similarly to fluid passage member302 of this embodiment.

Next, description will be given of another embodiment of a hydrauliccircuit structure in rear transaxle apparatus 20 shown in FIG. 19. Inthis embodiment, a downwardly open and substantially vertical fluidpassage 310 is bored, and the upper end of fluid passage 310 isconnected to kidney port 262 b opening at motor mounting surface 260 m.A substantially vertically fluid passage member 311 penetrated by asubstantially vertical fluid passage is slidably rotatably insertedupward through an O-ring into an opening 352 a penetrating a bottomsurface of a lower housing half 352, and the upper end of fluid passagemember 311 is slidably rotatably fitted into the lower end opening offluid passage 310 so as to connected the substantially verticalpenetrating fluid passage in fluid passage member 311 to fluid passage310. A connector 312 is screwed upward into the lower end of fluidpassage member 311 below the housing of rear transaxle 20, so thathydraulic hose 81 a can be connected to connector 312 so as to fluidlyconnect kidney port 262 b of hydraulic motor 240 to hydraulic motor 40in front transaxle 10.

On the other hand, a downwardly open and substantially vertical fluidpassage 313 is bored in center section 260, and the upper end of fluidpassage 313 is connected to fluid passage 304 connected to kidney port261 b opening at pump mounting surface 260 p (through fluid passage 305,as shown in FIG. 14). A substantially vertically fluid passage member314 penetrated by a substantially vertical fluid passage is slidablyrotatably inserted through an O-ring into an opening 352 b penetratingthe bottom surface of lower housing half 352, and the upper end of fluidpassage member 314 is slidably rotatably fitted into the lower endopening of fluid passage 313 so as to connect the substantially verticalfluid passage in fluid passage member 314 to fluid passage 313. Aconnector 315 is screwed upward into the lower end of fluid passagemember 314 below the housing of rear transaxle 20, so that hydraulichose 81 b can be connected to connector 315 so as to fluidly connectsecond kidney port 261 b of hydraulic pump 230 to hydraulic motor 40 infront transaxle 10. The other members are constructed in the same way asthe above-mentioned embodiment shown in FIG. 16.

Due to this structure, as shown in FIG. 19, when viewed in plan, thefluid passages in fluid passage members 311 and 314 are offset fromfilter 350 without manifold block 268, thereby vertically miniaturizingrear transaxle apparatus 20. Furthermore, fluid passage members 311 and314 are used for simply constructing hydraulic ports for fluidlyconnecting hydraulic pump 230 and motor 240 in rear transaxle 20 tohydraulic motor 40 in front transaxle 10. Fluid passage members 311 and314 can be rotated against center section 260 and lower housing half 352so as to adjust the directions of connectors 312 and 315, therebyoptimizing the piping of hydraulic hoses 81 a and 81 b.

Description will now be given of a hydraulic circuit structure accordingto a second embodiment, wherein hydraulic motor 40 in front transaxleapparatus 10 and hydraulic motor 240 in rear transaxle apparatus 20 arefluidly connected in parallel to hydraulic pump 230.

As shown in FIG. 20, in a horizontal portion of a center section 360 arebored a first kidney port 361 a and a second kidney port 361 b oppositeto each other. These kidney ports 361 a and 361 b are open at a positionwhere openings of the cylinder bores of cylinder block 233 pass.

On the other hand, as shown in FIG. 23, in the vertical portion of thecenter section 360 are bored a first kidney port 362 a and a secondkidney port 362 b opposite to each other. These kidney ports 362 a and362 b are open at a position where openings of the cylinder bores ofcylinder block 243 pass.

As shown in FIGS. 21, 22, and 24, in the center section are bored anupper first fluid passage 371 and a lower second fluid passage 372parallel to each other in the longitudinal direction of center section360.

As shown in FIG. 21, in center section 360 is bored a third fluidpassage 373 perpendicular to first fluid passage 371 so as to beconnected to first fluid passage 371. An opening of third fluid passage373 on a side surface of the center section 360 is closed by a plug 373a.

As shown in FIG. 22, in center section 360 are bored a slant fourthfluid passage 374, which connects second kidney port 361 b to secondfluid passage 372. An opening of fourth fluid passage 374 on the sideface of center section 360 is closed by a plug 374 a.

Moreover, as shown in FIGS. 21 to 23, a manifold block 368 is attachedto the undersurface of center section 360. From a side surface ofmanifold block 368 are bored a fifth fluid passage 375 and a sixth fluidpassage 376 forward and backward parallel to each other andperpendicular to first and second fluid passages 371 and 372. Caps 385and 386 are fitted into respective openings of fifth and sixth fluidpassages 375 and 376 so as to form respective connection ports 375 a and376 a. As shown in FIGS. 21 and 22, ends of caps 385 and 386 opposite tomanifold block 368 project outward from a lower housing half 347 so asto be connected to hydraulic hoses (not shown) outside lower housinghalf 347. Axes of connection ports 375 a and 376 a are disposed in asubstantially horizontal plane (i.e., a plane which is oriented neitherupward nor downward) so as to facilitate piping thereto. However, if theminimum requirement is achieved that heads of caps 385 and 386 on thehousing of rear transaxle apparatus 20 mounted on the vehicle areprevented from interfering with surrounding instruments, ports 375 a and376 a are accepted to be disposed on any of top, bottom, front, rear,left and right end surfaces of the housing and in any direction.

Between center section and manifold block 368 are bored a verticalseventh fluid passage 377 (FIG. 21), which connects a junction pointbetween second and fourth fluid passages 372 and 374 to fifth fluidpassage 375, and a vertical eighth fluid passage 378 (FIG. 22), whichconnects third fluid passage 373 to sixth fluid passage 376.

Due to the above mentioned fluid passage structure, hydraulic motor 40in front transaxle apparatus 10 and hydraulic motor 240 in reartransaxle apparatus 20 are fluidly connected in parallel to thehydraulic pump 230.

That is, as shown in FIG. 2, cap 54 a provided in front transaxleapparatus is connected to cap 385 provided in rear transaxle apparatus20 through a hydraulic hose 81 a, and cap 54 b in front transaxleapparatus 10 to the cap 386 in rear transaxle apparatus 20 through ahydraulic hose 81 b, thereby forming a hydraulic circuit shown in FIG.25.

According to the hydraulic circuit shown in FIG. 19, in center section361 a arranged in rear transaxle apparatus 20, the first kidney port361, formed to pump mounting surface 360 p, is connected through firstfluid passage 371 to first kidney port 362 a and to motor mountingsurface 360 m. First kidney port of 361 a, formed in center section 361a to pump mounting surface 360 p, is connected to first kidney port 62a, formed to the motor mounting surface 63 m, through a string of fluidpassages 399 a, which branch from first fluid passage 371 (as shown inFIG. 25) and consist of third fluid passage 373, sixth fluid passage376, hydraulic hose 81 a, and first fluid passage 53 a provided incenter section 62 of front transaxle apparatus 10.

On the other hand, in the center section arranged in the rear transaxleapparatus, the second kidney port 362 b formed to the motor mountingsurface 360 m is connected to the second kidney port 361 b formed to thepump mounting surface 360 p through a string of fluid passage 399 bwhich consists of the second fluid passage 372 and fourth fluid passage374.

Moreover, since the fourth fluid passage 374 is connected to the seventhfluid passage 377, the second kidney port of 361 b formed to the pumpmounting surface 360 p is connected to the second kidney port 62 bformed to the motor mounting surface 63 m through a string of the fluidpassage 399 c which consists of the fourth fluid passage 374, theseventh fluid passage 377, and the fifth fluid passage 375 (as shown inFIG. 25), hydraulic hose 81 b, and second fluid passage 53 b provided incenter section 62 of front transaxle apparatus.

In this way, in the hydraulic circuit structure according to the secondembodiment, hydraulic motors 40 and 340 arranged in respective front andrear transaxle apparatuses 10 and 20 are fluidly connected in parallelto hydraulic pump 230. Particularly, in this parallel connectionstructure is suitable for a vehicle which turns left and right whilegenerating a difference in rotary speed between the front wheels and therear wheels.

Due to the above structure, in front transaxle apparatus and reartransaxle apparatus 10 are driven front wheel axles 12L and 12R and rearwheel axles 22L and 22R, respectively, thereby making a four-wheel-drivevehicle which excels in steering performance and running performanceover bad ground conditions.

Alternatively, although not shown, caps 385 and 386 may be plugged so asto make a rear-wheel-drive vehicle which drives with only the drivingforce of hydraulic motor 340 of rear transaxle apparatus 20.

Moreover, as shown in FIG. 25, the vehicle provided with the in parallelhydraulic connection structure may be modified by providing differentialgear units 120 and 220 in front and rear transaxle apparatuses 10 and 20with respective differential-lock devices 125 and 225 for restrictingdifferential rotation of right and left axles and by providing operationlevers for differential-lock devices 125 and 225 on the vehicle, so asto restrict the differential rotation of the axles when any of therunning wheels are stuck.

In the in parallel connection, hydraulic fluid is distributed betweenthe two hydraulic motors 40 and 340, whereby a larger amount ofhydraulic fluid flows to the lighter-loaded of the hydraulic motors 40and 340. For this reason, when a right front wheel actuated by hydraulicmotor 40 is stuck, for example, the vehicle becomes impossible to freebecause hydraulic fluid doesn't flow to hydraulic motor and the rearaxles aren't actuated; by operating differential-lock device 125, loadfor driving a left front wheel is applied to hydraulic motor 40 so as tosupply a suitable amount of hydraulic fluid to rear hydraulic motor 340so as to drive the rear wheels, thereby enabling the vehicle to befreed.

Incidentally, in the case where differential-lock devices 125 and 225are provided to respective front and rear transaxle apparatuses 10 and20, a common differential-lock pedal may be provided for both thedifferential-lock devices so as to actuate the devices simultaneously,or two pedals may be separately provided for the respectivedifferential-lock devices.

Description will be given of a second embodiment of the working vehiclehaving rear transaxle apparatus 20.

As shown in FIG. 26, in the working vehicle according to the secondembodiment, a pair of left and right front transaxle apparatuses 400Land 400R are provided to front frame 11. Left and right front transaxleapparatuses 400L and 400R include respective front-wheel axles 412L and412R, and are fluidly connected to rear transaxle apparatus 20 through adistribution device 80, hydraulic hoses, etc.

As shown in FIG. 27, an upper housing half 446 and a lower housing half447 are joined to each other so as to form a housing of each of fronttransaxle apparatuses for incorporating a hydraulic motor. Left andright front transaxle apparatuses 400L and 400R share the same structureand are supported on front frame 11 through respective stays 19 a and 19b so as to orient front-wheel axles 412L and 412R opposite to eachother.

As shown in FIG. 28, each of the front transaxle apparatuses 400L and400R incorporates a hydraulic motor 440, which is fluidly connected tohydraulic pump 230 in rear transaxle apparatus 20 (not shown). Rotationof a motor shaft 441 of hydraulic motor 440 is output to the outside ofthe housing through each of front wheel axles 412L and 412R.

As shown in FIG. 28, into each of front transaxle apparatuses isintegrally assembled hydraulic motor 440, which is so constructed that acylinder block 443 is rotatably slidably mounted on a motor mountingsurface 463 m formed on a vertical portion of a center section 462. Aplurality of pistons 442 are reciprocally movably fitted into aplurality of cylinder bores in cylinder block 443 through respectivebiasing springs. The heads of pistons 442 abut against a fixed swashplate 444 which is fixedly sandwiched between upper housing half 446 andlower housing half 447. An opening 444 b is provided in the center offixed swash plate 444 so as to allow motor shaft 441 to passtherethrough.

So that motor shaft 441 may function as an output shaft, motor shaft 441is rotatably supported by a sealed bearing 445 which is sandwichedbetween upper housing half 446 and lower housing half 447, and isnot-relatively rotatably engaged with cylinder block 443 so as to bedisposed horizontally on the rotary axis of cylinder block 443.

Thus, an axial piston type fixed displacement hydraulic motor isconstructed in each of front transaxle apparatuses.

Moreover, as shown in FIG. 28, a pair of first and second kidney ports462 a and 462 b are formed in a vertical portion of center section 462from a motor mounting surfaces 463 m. A first fluid passage 453 a and asecond fluid passage 453 b are horizontally formed in center section 462so as to be fluidly connected to respective kidney ports 462 a and 462b. First fluid passage 453 a and second fluid passage 453 b areconnected to respective caps 454 a and 454 b to be connected torespective hydraulic hoses. Thus, each of hydraulic motors is fluidlyconnected to the hydraulic pump 230 in rear transaxle apparatus throughthe hydraulic hoses (not shown).

Although not shown, a bypass operation lever for opening first fluidpassage 453 a and second fluid passage 453 b to the fluid sump isincluded with each front transaxle apparatuses so as to idle front wheelaxles 412L and 412R when the vehicle is towed.

As shown in FIG. 28, on an end portion of motor shaft 441 opposite tothe center section 462 is provided a drive output gear 431 in splinefitting, whereby drive output gear 431 rotates integrally with motorshaft 441. On a portion of drive output gear 431 toward center section462 is integrally formed a brake rotor 433 whose diameter is larger thanthat of drive output gear 431, so that rotating motor shaft 441 isbraked by pressing brake rotor 433 between brake pads 434 a and 434 b.

Moreover, as shown in FIG. 28, bearing 439 a and 439 b rotatably supportfront-wheel axle 412L (or 412R) in parallel to motor shaft 441. Adeceleration gear 421 is fixed onto front-wheel axle 412L (or 412R) andengages with drive output gear 431. The diameter of deceleration gear421 is larger than drive output gear 431 so as to reduce the rotaryspeed of motor shaft 441 greatly so as to enable each of front transaxleapparatuses to incorporate a hydraulic motor having a small capacity.

Alternatively, although not shown, instead of front-wheel axle 412L (or412R), upper and lower housing halves 446 and 447 may be formed on aside thereof opposite to the center section 462 with an opening on anaxial extension of motor shaft 441, and motor shaft 441 may be extendedthrough the opening to the outside of the housing so as to be fixed tofront wheel 13. In brief, motor shaft 441 may replace front wheel axle412L (or 412R).

As shown in FIG. 26, front transaxle apparatuses constructed asdescribed above are fluidly connected to rear transaxle apparatusthrough distribution device 80, hydraulic hoses, etc., so as to driverespective front-wheel axles 412L and 412R, thereby rotating left andright front wheels 13.

There are several types of fluidal connection between front transaxleapparatuses 400L and 400R and rear transaxle apparatus 20. These fluidalconnection types will be described as follows.

According to an embodiment shown in FIG. 29, employing rear transaxleapparatus according to the first embodiment (shown in FIGS. 8 to 11),hydraulic motor 240 of rear transaxle apparatus and a circuit, whichfluidly connects in parallel hydraulic motors 440 of both fronttransaxle apparatuses 400L and 400R to each other, are fluidly connectedin series to the hydraulic pump of rear transaxle apparatus.

Due to this structure, front-wheel axles 412L and 412 of front transaxleapparatuses can be driven differentially.

According to an embodiment shown in FIG. 30, employing a fluidalconnection similar to that of FIG. 29, both hydraulic motors 440 offront transaxle apparatuses 400L and 400R are variable displacementhydraulic motors having respective movable swash plates 444 c. Thisstructure is particularly effective for a vehicle having an Ackermantype steering device or chassis layout wherein a difference in rotaryspeed is generated between the front wheels and the rear wheels at thetime of turning of the vehicle, namely, that coupling part 50 is notlocated at an equidistant position from both front and rear axles,because a difference of rotary speed can be generated between front andrear wheels by adjusting movable swash plates 444 c so as to improvesteering performance of the vehicle.

According to an embodiment shown in FIG. 31, employing rear transaxleapparatus according to the first embodiment, hydraulic motor 240 of reartransaxle apparatus 20 and hydraulic motors 440 of both front transaxleapparatuses 400L and 400R are all fluidly connected in series tohydraulic pump 230 of transaxle apparatus 20. Moreover, both hydraulicmotors 440 of front transaxle apparatuses 400L and 400R are variabledisplacement hydraulic motors having respective movable swash plates 444c.

This structure is particularly effective for a vehicle having anAckerman type steering device or a chassis layout wherein a differencein rotary speed is generated between the front wheels and the rearwheels at the time of turning of the vehicle, namely, that coupling part50 is not located at an equidistant position from both front and rearaxles, because a difference in rotary speed can be generated betweenfront and rear wheels by adjusting movable swash plates 444 c so as toimprove steering performance of the vehicle.

According to a hydraulic circuit shown in FIG. 32, employing reartransaxle apparatus according to the second embodiment (shown in FIGS.20 to 24), hydraulic motor 340 of rear transaxle apparatus 20 andhydraulic motors 440 of both front transaxle apparatuses are all fluidlyconnected in parallel to hydraulic pump of rear transaxle apparatus.

Due to this structure, front-wheel axles 412L and 412 of front transaxleapparatuses can be driven differentially.

Moreover, the hydraulic circuit in rear transaxle apparatus 20 isfluidly connected to the hydraulic circuit of front transaxle 400L and400R apparatuses through a control valve 80 a. If any of front wheels 13is stuck, control valve 80 a stops the supply of hydraulic fluid tofront transaxle apparatuses 400L and 400R, and hydraulic motor 340rotates rear wheel axles 22L and 22R, whereby the vehicle is freed.Furthermore, differential-lock device 225 is provided to restrict thedifferential rotation of rear wheel axles 22L and 22R so as tocorrespond to the situation where one of rear wheels 23 is stuck.

According to an embodiment shown in FIG. 33, employing rear transaxleapparatus 20 according to the second embodiment, hydraulic motor 340 ofrear transaxle apparatus 20 and a circuit, which fluidly connects inseries hydraulic motors 440 of both front transaxle apparatuses 400L and400R to each other, are fluidly connected in parallel to hydraulic pumpof rear transaxle apparatus in parallel. Moreover, both hydraulic motorsof front transaxle apparatuses 400L and 400R are variable displacementhydraulic motors having respective movable swash plates 444 c.

This structure is particularly effective for a vehicle having anAckerman type steering device or a chassis layout wherein a differencein rotary speed is generated between the front wheels and the rearwheels at the time of turning of the vehicle, namely, that coupling part50 is not located at an equidistant position from both front and rearaxles, because a difference in rotary speed can be generated betweenfront and rear wheels by adjusting movable swash plates 444 c so as toimprove steering performance of the vehicle.

Description will now be given of a layout of front transaxleapparatuses.

As shown in FIG. 27, inner ends of front wheel axles 412L and 412R,which are opposite to respective front wheels 13, are inserted inrespective front transaxle apparatuses 400L and 400R.

Front transaxle apparatuses are supported on left and right sideportions of front frame 11 through stays 19 a and 19 b, respectively, soas to ensure a lateral interval 401L between both front transaxleapparatuses 400L and 400R.

This interval 401L is wider than a lateral width 402L of secondworking-device drive transmission belt 59 at the position where belt 59passes front transaxle apparatuses.

With arranging front transaxle apparatuses 400L and 400R as describedabove, even if a working device such as mower device 3 is raised so asto change the vertical height where second working-device drivetransmission belt 59 passes, second working-device drive transmissionbelt 59 interferes with neither front wheel axles 412L and 412R norfront transaxle apparatuses. Therefore, the problem of secondworking-device actuation transmission belt 59 rubbing against frontwheel axle 412L, 412R, etc., and wearing out is not generated.

1. A transaxle apparatus, comprising: a housing; a hydrostatictransmission disposed in said housing, said hydrostatic transmissionincluding a hydraulic pump receiving power from a prime mover, a firsthydraulic motor driven in response to fluid supplied from said hydraulicpump, and a center section including an inner fluid passage for fluidlyconnecting said first hydraulic motor to said hydraulic pump; a firstaxle disposed in said housing and driven by said first hydraulic motor;and a hydraulic actuator disposed outside said housing so as to drive asecond axle disposed outside said housing, wherein said center sectionincludes a flexible port disposed in a surface of said housing andfluidly connected to said inner fluid passage so as to supply hydraulicfluid flowing in said inner fluid passage to said hydraulic actuatordisposed outside said housing, and wherein said flexible port has adirectionally adjustable connection portion to which a piping to saidhydraulic actuator is connected.
 2. The transaxle apparatus as set forthin claim 1, wherein said hydraulic actuator disposed outside saidhousing is a second hydraulic motor.
 3. The transaxle apparatus as setforth in claim 1, wherein said center section is detachably attached tosaid housing.
 4. The transaxle apparatus as set forth in claim 2,wherein said center section is detachably attached to said housing. 5.The transaxle apparatus as set forth in claim 3, wherein said port isequipped with a tubular element, and said housing has an opening forexposing an utmost end of said tubular element to an area outside of thehousing.
 6. The transaxle apparatus as set forth in claim 4, whereinsaid port is equipped with a tubular element, and said housing has anopening for exposing an utmost end of said tubular element to an areaoutside of the housing.
 7. The transaxle apparatus as set forth in claim5, wherein said tubular element is detachably attached to said centersection.
 8. The transaxle apparatus as set forth in claim 6, whereinsaid tubular element is detachably attached to said center section. 9.The transaxle apparatus as set forth in claim 2, wherein said portfluidly connects in parallel said first hydraulic motor and said secondhydraulic motor to said hydraulic pump.
 10. The transaxle apparatus asset forth in claim 2, wherein said port fluidly connects in series saidfirst hydraulic motor and said second hydraulic motor to said hydraulicpump.
 11. A vehicle, comprising: a first frame disposed at either afront or a rear portion of said vehicle; a prime mover mounted on saidfirst frame; a first transaxle apparatus mounted on said first frame,said first transaxle apparatus including an input shaft receiving powerfrom said prime mover, a pair of first axles, and a hydrostatictransmission, wherein said hydrostatic transmission includes a hydraulicpump driven by rotating said input shaft and discharging fluid variablyin quantity and direction, a first hydraulic motor for driving saidfirst axles, a fluid passage fluidly connecting said hydraulic pump tosaid hydraulic motor, a second frame disposed at the other of said frontor rear portions of said vehicle; a second transaxle apparatus mountedon said second frame, said second transaxle apparatus including a pairof second axles; and a coupling part for coupling said first and secondframes to each other so that said first and second frames are rotatablearound a vertical axis relative to each other according to a steeringoperation, wherein said hydrostatic transmission of said first transaxleapparatus includes a flexible port disposed in a surface of said housingand fluidly connected to said fluid passage, the flexible port having adirectionally adjustable connection portion, and wherein said secondtransaxle apparatus includes a second hydraulic motor fluidly connectedto said connection portion of said flexible port so as to drive saidpair of second axles.
 12. The vehicle as set forth in claim 11, whereinsaid hydrostatic transmission is incorporated in said first transaxleapparatus.
 13. The vehicle as set forth in claim 11, wherein said portfluidly connects in series said first and second hydraulic motors tosaid hydraulic pump.
 14. The vehicle as set forth in claim 11, whereinsaid port fluidly connects in parallel said first and second hydraulicmotors to said hydraulic pump.
 15. The vehicle as set forth in claim 11,wherein a working device is disposed adjacent to a distal side of one ofsaid first and second frame, wherein a rotor for receiving power fromsaid prime mover is disposed so as to coincide a rotary axis of saidrotor with said vertical axis, wherein at least either said pair offirst axles or said pair of second axles nearer to said working devicehave different lengths, and wherein a transmission element drivinglyconnecting said rotor to said working device crosses a longer axle ofsaid pair of first or second axles nearer to said working device.